1. Field of the Invention
This invention relates to an eye refractive power measuring apparatus for alleviating the adjusting power of an eye to be examined and measuring the refractive power of the eye.
2. Description of the Prior Art
Generally, when the refractive power of an eye is to be measured, it is a rule to effect the measurement in a state in which the adjusting power of the eye to be examined is loosened. However, where a target image to which the examinee's line of sight is to be fixed is optically formed in a light-intercepting housing and the examinee is caused to see this target image as has heretofore been practiced, the state of so-called mechanical near-sightedness is often brought about by the adjusting power being caused to come into play by looking into the target image.
In order to avoid such a state, various means to which the means called the cloud-mist type is applied have heretofore been developed and incorporated into an eye refractive power measuring apparatus. However, in the apparatus of this type, convex lenses must be loaded by an appropriate amount corresponding to the refractive power of the eye to be examined and if too many convex lenses are used, there may be brought about a reverse effect. Moreover, it is difficult to apply appropriate cloud-mist to the refractive power of the eye to be examined which is not yet known, and in addition, the eye to be examined widely ranges from intense shortsightedness exceeding -10 diopters to a lens-free eye exceeding +10 diopters. The amount of mechanical short-sightedness occurring when the eye to be examined looks into the target image may vary greatly with age or different individuals and it is more difficult to apply appropriate cloud-mist to the refractive power of such eye. Accordingly, to apply appropriate cloud-mist, it becomes necessary to correct the position of the target image with the value of refraction measured under predetermined conditions as a reference.
However, the problem is the relation between the speed at which the position of the target image is corrected and the responsiveness of the eye to be examined. That is, if the position of the target image is changed fast, the examinee cannot know what has happened, and the state of adjustment of the eye will not vary or a contrary result will be brought about. Conversery, if the target image is moved slowly, too much time will be required and this will impart an extra burden to the examinee and, in the meantime, his line of sight will fluctuate and make accurate measurement impossible.